1. Field of the Invention
The present invention relates to a three-valves manifold for use in a differential pressure type flow meter for introducing a differential pressure to a differential pressure oscillator.
2. Related Art Statements
In case of measuring a flow rate by using a differential pressure type flow meter, as illustrated in FIG. 4, an orifice 2 is arranged within a main conduit 1 through which a fluid whose flow rate is to be measured flows, and one ends of pressure guide pipes 4a and 4b are connected to the main conduit 1 at downstream and upstream positions, respectively with respect to the orifice 2. The other ends of the pressure guide pipes 4a and 4b are coupled with a differential pressure transducer 5. Since the differential pressure transducer 5 generates a signal representing a differential pressure, the differential pressure transducer 5 is also called a differential pressure signal generator in the present specification.
The pressure guide pipes 4a and 4b are communicated with each other by means of a connecting pipe 7. In the pressure guide pipes 4a and 4b and connecting pipe 7 there are arranged valves 6a, 6b and 6c, respectively. The above mentioned pressure guide pipes 4a, 4b and connecting pipe 7 and the valves 6a, 6b and 6c are constructed as a single unit named a three-valves manifold.
Upon measuring a flow rate of the fluid flowing through the main conduit 1, the valves 6a and 6b are opened and the valve 6c is closed to introduce a pressure of the main conduit 1 at the upstream position with respect to the orifice 2 as well as a pressure of the main conduit 1 at the downstream position with respect to the orifice 2 to both sides of a pressure sensitive member of the differential pressure signal generator 5. In this manner, a differential pressure is applied to the differential pressure signal generator 5 to generate a signal representing a flow rate of the fluid passing through the main conduit 1. Upon adjusting a zero point of the differential pressure signal generator 5, the valve 6c is opened and both the valves 6a and 6b are closed such that a pressure at one side of the pressure sensitive member of the differential pressure signal generator 5 becomes identical with a pressure at the other side of the pressure sensitive member of the differential pressure signal generator 5.
When the differential pressure type flow meter is used initially or is used again after a rather long intermission, it is important to operate the valves 6a-6c carefully such that an excessively high pressure is not applied to only one side of the pressure sensitive member of the differential pressure signal generator 5. To this end, one of the valves 6a and 6b is opened and the valve 6c is opened. After that, the other of the valves 6a and 6b is opened and the valve 6c is closed to initiate a measurement of a flow rate.
In this manner, during the measurement, at the time of initial use and at the time of use after long intermission, the three valves 6a-6c are opened and closed in accordance with a predetermined manner. If the valves 6a-6c are erroneously operated, a pressure of the fluid flowing through the main conduit 1 might be applied to only one side of the pressure sensitive member of the differential pressure signal generator 5 and the differential pressure signal generator 5 might be broken. Furthermore, a sealing liquid contained within the pressure guide pipes 4a and 4b might be introduced into the main conduit 1. The above mentioned problems also occur in the three-valves manifold in which the pressure guide pipes 4a and 4b and the three valves 6a-6c are formed as a single unit.